1. Field of the Invention
The present invention relates to a printed wiring board having a through-hole conductor formed by filling plating in a penetrating hole in an insulative substrate, and to its manufacturing method.
2. Discussion of the Background
In Japanese Patent Publication No. 4248353, a filling method is described for filling a penetrating hole for a through-hole conductor by plating. In Japanese Patent Publication No. 4248353, an electrolytic plating solution is used, whose speed of deposition onto the inner wall of a penetrating hole is faster than the speed of deposition onto the substrate surface. As shown in FIG. 1 of Japanese Patent Publication No. 4248353, a metal layer around the middle of a through hole is formed to be thicker than a metal layer around an opening portion of the through hole so that the portion around the middle will become the narrowest of the through hole. Furthermore, by continuing electrolytic plating, plating is deposited to plug the narrowest portion, and a through-hole conductor is formed. However, if the filling method in Japanese Patent Publication No. 4248353 is used, the narrowest portion, which is positioned around the middle of a through hole and is made of electrolytic plated film, has a cross-sectional V-shape, namely, a portion with an acute angle. Accordingly, when the narrowest portion of the through hole is plugged and then electrolytic plating is performed, performance of the plating solution may decrease at the acute-angle portion, leaving a void at the acute-angle portion. The contents of this publication are incorporated herein by reference in their entirety.